The present invention relates to a capacitive sensor for measuring material properties such as moisture or for detecting the presence or proximity of an object.
Most capacitive sensors for measuring material properties use a parallel plate or concentric cylinder design. The sensors work well in the laboratory or in a continuous stream of material, but certain applications require a less obtrusive sensor. Proximity sensors may be used to measure the dielectric properties of an object without entering or penetrating the object.
Proximity detectors typically measure capacitance between one conductor and ground and detect the presence of an object by noting the change in sensor capacitance when the object comes within the electric field generated between the sensor and a. reference potential. To measure in only one direction, such a sensor will typically be shielded on one side with a reference potential. This prevents observing objects on the shielded side but introduces a large measured capacitance which diminishes the sensitivity of the sensor.